1. Field of Invention
The present invention concerns a cleaner using ultra-pure water, and particularly a cleaner for use in the wet cleaning process for the semiconductor industry.
2. Discussion of the Related Art
It has been devised to introduce, just before the point of use, an ion absorption film module filled with a porous film of 0.01 to 1 xcexcm in average hole diameter, the porous film holding polymer chains having a cation exchange group, an anion exchange group and a chelating group (hereafter, called cation absorption film, anion absorption film and chelate film, respectively); and each such film being generically called an ion absorption film for reducing impurities such as heavy metals, for example, just before the point of use (Japanese Patent Laid-Open No. HEI 8-89954).
A hollow yarn film module having a cation exchange group associated therewith is applied to eliminate metals, and it is particularly effective in eliminating alkali metals and/or alkali earth metals. A hollow yarn film module having an anion exchange group can effectively eliminate particles and colloidal matter. A hollow yarn film module having a chelating group has an excellent function of eliminating heavy metal material, even when present at an extremely low concentration.
It is known that the use of hydrogenated ultra-pure water can suppress and/or eliminate deposition onto a substance of silicon or the like. Further, Japanese Patent Laid-Open No. HEI 9-10713 discloses a method including the steps of presenting an extremely high hydrocarbon elimination rate and by treating the wafer with ultra-pure water in order to perform substrate hydrogen termination, the ultra-pure water containing hydrogen or a mixture of hydrogen and a rare gas. As hydrogenated ultra-pure water presents an extremely high hydrocarbon elimination rate, using a rinse of hydrogenated ultra-pure water should allow a cleaner wafer surface to be obtained than possibly achieved using a rinse not employing hydrogenated ultra-pure water.
However, through the comparison between a film (for example, an insulation film such as a gate insulation film) formed on the silicon substrate when hydrogenated ultra-pure water is used to rinse and a film formed on the substrate when non-hydrogenated ultra-pure water is used to rinse, the Inventors have found a problem that the former film happens to be inferior to the latter film in quality (for example, dielectric strength).
They have investigated the cause thereof and have found that the hydrogenated ultra-pure water is capable of eliminating particles and/or of preventing particles from depositing on a substrate, but also has a function of facilitating deposition of metallic impurities onto the substrate. They have explicated that this deposition provokes film quality degeneration (for example, deterioration of dielectric strength).
The present invention provides a wet cleaning apparatus for eliminating a trace heavy metal, colloidal matter, and/or other impurities contained in ultra-pure water used as rinse water in the semiconductor cleaning process and suppressing deposition of impurities, such as particles and/or heavy metals that degenerate device characteristics, onto the substance surface.
According to the present invention, a wet cleaning apparatus for rinsing with ultra-pure water includes a piping through which is supplied to a point of use inside the apparatus, the piping being provided with a module filled with a porous film in which polymer chains having at least one of a cation exchange group, an anion exchange group and a chelating group held within the polymer chains, the porous film being positioned in the middle of the piping.
Here, the cleaner is a multi-tank type, a single tank type batch cleaner, or a sheet cleaner for performing wet cleaning. In wet cleaning, the cleaner is an apparatus for cleaning a wafer surface with ultra-pure water-based chemicals, for rinsing surface chemical deposits therefrom with the ultra-pure water and eventually for drying the wafer surface. Note that such an apparatus includes a cleaner for cleaning by ultra-pure water jet.
Here, the cleaner includes a wet bench. A wet bench is a cleaning place provided with exhaust equipment and cleaning equipment. The cleaning equipment is provided with ultra-pure water, chemical supply piping, and drain piping for cleaning liquid and rinse water.
Ultra-pure water produced by the ultra-pure water system always circulates within the main loop and is extracted as necessary from the main loop by means of a branch piping to dilute chemicals necessary for cleaning or rinsing, as appropriate.
Branch piping is introduced into the cleaner or wet bench to supply ultra-pure water for individual cleaning processes, and among them, in the final rinse corresponding to the final process of the cleaning processes, it is an object to eliminate any chemical deposit from the semiconductor substrate that would otherwise exist thereon after cleaning.
Here, the final rinse designates the process for rinsing a chemical deposit on the wafer surface with ultra-pure water or hydrogenated ultra-pure water just before a wafer drying process, such as IPA (2-propanol) vapor drying, spin drying, or Marangoni-type drying.
As the rinse with ultra-pure water itself does not present an effect to suppress deposition of impurities such as various types of metal, rinsing water after chemical cleaning should be free from even a trace of impurities.
Especially, in the last process of wet cleaning, the substrate surface is etched with dilute hydrofluoric acid solution, a bare silicon surface, deprived of an oxide film, is exposed, and thereafter, the rinse process is performed with ultra-pure water.
There, the object of ultra-pure water rinse is to eliminate hydrofluoric acid chemical deposited on the substrate by rinsing with ultra-pure water. However, if impurities such as metals exist in the ultra-pure water, the use thereof can result in impurity deposition since the silicon surface is exposed. Once impurities deposit onto the substrate, the ultra-pure water is totally incapable of eliminating them. Consequently, the ultra-pure water used for the final rinse is required to be totally free from impurities such as metals that tend to deposit onto the substrate surface.
Among impurities present in the ultra-pure water, especially metals, are reduced and hardly detected, even by means of a high sensitivity instrument analyzer such as an inductively coupled plasma analyzer (ICP-MS).
It is presumed that the presence of impurities under the analyzer quantification lower limit level provokes the deposition of impurities onto the substrate surface.
Almost all metals existing in the ultra-pure water are generally anionized. However, it is presumed that they do not exist as independent anions, but they are clustered or colloidalized, forming electrostatically weak binding with silica or organic matter having negative charge. For this reason, it is difficult to remove the clustered matter having weak charge and small size with ion exchange or reverse osmosis equipment designed to remove metal impurities in the ultra-pure water system. It has been found that these metal impurities are present at the exit of ultra-pure water system and may deposit onto the substrate surface.
Here, the investigation by the Inventors has shown that the use of a module filled with an ion absorption film holding polymer chains having at least have of a exchange group, an anion exchange group and a chelating group can eliminate impurities, such as a clustered metal, that could not be removed by the conventional system.
Here, as the ion absorption film used in the present invention, for example, a hollow yarn porous film of 0.01 to 1 xcexcm in average hole diameter is used preferably, the porous film containing polymer chains having ion exchange groups inside the film, the ion exchange groups forming 0.2 to 10 mili-equivalent weight per 1 gram of film. The manufacturing method and other details thereof are as described in the document JAPANESE PATENT LAID-OPEN NO. HEI 8-89954.
As for ion absorption film, for example, it concerns one having quaternary anime as an exchange group, and quaternarized chloromethyl styrene is generally used. However, those obtained by quaternarizing azote atoms of pyridine-based or imidazole-based heterocyclic rings can also be used.
As for a potential cation absorption film, a sulfonic group, phosphoric group, carboxylic group or the like are advantageously used as the exchange group.
Concerning a usable chelating group, an iminodi acetic group, mercapto group, ethylene diamine or the like can be used as the exchange group.
As a wet cleaning method in the semiconductor production, a cleaning method called RCA cleaning, shown in FIG. 1, has been used conventionally. This RCA cleaning is characterized by blending acid or alkali on the base of hydrogen peroxide, and cleaning at a high temperature, and repeating ultra-pure water rinsing following chemical cleaning.
The role of ultra-pure water rinse is nothing other than the removal of used chemicals from the substrate. However, as the rinse process hardly removes impurities other than the chemical solution, it is required to supply cleaned ultra-pure water. Especially, if the contamination occurs in the final rinse, all cleaning processes should be performed over again. Consequently, it is necessary to take some measures against recontamination.
In order to improve the quality of ultra-pure used for a final rinse, the problem of ineffective cleaning in the wet cleaning can be resolved by integrating these ion absorption film modules into the ultra-pure water piping for final rinse in a cleaner.
In a cleaner according to the present invention, ultra-pure water is first treated by a module filled with ion absorption film holding polymer chains having at least one of a cation exchange group. An anion exchange group and a chelating exchange group acting as an exchange group inside the film when hydrogenated ultra-pure water is used in the rinse process of wet cleaning, and then hydrogenated, for instance, when a silicon wafer is to be washed for semiconductor manufacturing.
Hydrogenated ultra-pure water is capable of eliminating particles deposit from a substrate and has an effect to prevent particles from depositing on the substrate, but when metallic impurities are present, it facilitates disadvantageously the deposition of such metallic impurities onto the substrate.
It was found that metal deposition onto the substrate can be suppressed even if hydrogenated ultra-pure water is used, provided that metal impurities present in the ultra-pure water can be reduced sufficiently.
Consequently, according to the present invention, the deposition of not only particles but also metal impurities can be suppressed. Besides, an insulation film having, for instance, a high dielectric strength can be formed on the substrate even when the final rinse is performed by the wet cleaning apparatus of the present invention.
Therefore, a cleaning method wherein ultra-pure water is hydrogenated after having sufficiently reduced metal impurities in the ultra-pure water through the treatment with a module filled with ion absorption films and a cleaner capable of carrying out that cleaning method have been invented.
Moreover, the ultra-pure water is first hydrogenated when hydrogenated ultra-pure water is used in the rinse process of wet cleaning and then treated by a module filled with an ion absorption film holding polymer chains having at least one of a cation exchange group, an anion exchange group and a chelating group as an exchange group inside the film, when a silicon wafer is to be washed for semiconductor manufacturing.
A combination of any two or more modules filled with an ion absorption film holding polymer chains having at least one of cation exchange group, an anion exchange group and a chelating group can be used in the cleaner or wet bench, when a silicon wafer is to be washed for semiconductor manufacturing.
As for the metal present in the ultra-pure water, though the metal itself is ionized and becomes cationic, matter like negatively charged silica or organic acid approaches around the metal, clusters and exists in a colloidal state.
As charge deviation varies according to the nature of the metal element paired with silica or organic matter, a complete removal may not be assured by a single film module. However, in such a case, the metal can be eliminated completely by combining films whereby different exchange groups are introduced. As a possible combination in one method, two kinds of films can be combined as follows:
Cation absorption film+anion absorption film;
Chelate film+anion absorption film;
Anion absorption film+cation absorption film;
Anion absorption film+chelate film;
Cation absorption film+chelate film; and
Chelate film+cation absorption film
and, in another method, three kinds of films can be combined as follows:
Cation absorption film+chelate film+anion absorption film;
Chelate film+cation absorption film+anion absorption film;
Cation absorption film+anion absorption film+chelate film;
Anion absorption film+cation absorption film+chelate film;
Anion absorption film+chelate film+cation absorption film; and
Chelate film+anion absorption film+cation absorption film. However, the combination preferably includes a chelate film to eliminate impurities.
Ultra-pure water hydrogenation can take place either upstream of the module or downstream of the module. If it is performed upstream, the metal deposition onto the substrate can be prevented more effectively. Note that the hydrogenated ultrapure water includes water hydrogenated from exterior and one containing hydrogen from the beginning of the manufacturing.